1. Field of the Invention
The present invention relates to an image forming apparatus that includes image-forming process cartridges arranged in tandem.
2. Description of the Related Art
Japanese Patent Application Laid-open No. H5-35042 discloses a color image forming apparatus including image-forming process cartridges arranged in tandem along a paper feed line and installable in an arbitrary order.
Japanese Patent Application Laid-open No. H10-171199 discloses a color electrophotographic apparatus that includes image-forming process cartridges each of which has a color identifying unit, arranged in tandem along a paper feed line. The color identifying unit identifies the color of the toner contained in the cartridge, and detects whether each cartridge is placed in a proper position, and displays a result of detection.
Japanese Patent Application Laid-open No. 2001-83862 discloses an image forming apparatus that includes a common image-forming process cartridges each of which has a memory unit, arranged in tandem along a paper feed line. The memory unit stores the color of the toner contained in the cartridge, and when each image-forming process cartridge containing each color is not positioned properly, the image forming apparatus does not start operation, or alarms the improper condition.
Japanese Patent Application Laid-open No. 2001-183886 discloses an image forming apparatus that includes image-forming process cartridges arranged in tandem along a paper feed line. An image-forming process cartridge of black is arranged upstream to other image-forming process cartridges in a direction of the paper feed line, and a toner retaining capacity thereof is expanded by stretching toward the upstream side.
Japanese Patent Application Laid-open No. 2002-14508 discloses an image forming apparatus that includes image-forming process cartridges arranged in tandem along the moving path of an intermediate transfer belt, that detects toner color information of the image-forming process cartridges installed in the respective positions, and that selectively supplies image data of the toner color detected to a print head at each installation position. Each image formed by each image-forming process cartridge is transferred onto the intermediate transfer belt from which the image is transferred onto paper.
Conventionally, various image forming apparatuses for forming a multicolor (two or more colors) image using, for example, an electrophotographic process are developed and are put to a practical use. The following is a technique common to those apparatuses. There are color toners of black (Bk), yellow (Y), magenta (M), and cyan (C). The position and the order in the tandem arrangement of developing units or image-forming units of the respective color toners are fixed, and the number of color toners to be used is also fixed for each apparatus. In other words, the apparatuses cannot be used in a condition appropriate for use desired by each user. Therefore the user needs to purchase another appropriate apparatus. For example, with a color copying machine, there are many inconveniences, such as the use of the color copying machine as a two-color fast copying machine of black and white, the use of a full-color developing unit for a two-color document (red and white, yellow and blue, black and yellow, etc.), the user being unable to build up own system by purchasing an optional unit (the system being fixed on colors), and the need for a maintenance even for unused colors. That is, specifications and functions have not been able to be customized for user.
To cope with the problems, the above conventional image forming apparatuses have been proposed. However, the ordinary tandem color image forming apparatus has limitations, such as the use of detachable transfer units in such a way as not to drive color cartridges (Y, M, C) in consideration of the life elongation in case of printing only in black, and the deposition of the process cartridge of black (Bk) in the farthest position so as not to affect the connection/disconnection of the transfer units in consideration of productivity. If the order in the tandem arrangement is set free as the technologies described in Japanese Patent Application Laid-open Nos. H5-35042 and 2002-14508, it becomes necessary to configure the apparatus such that all of the transfer units at image-forming process cartridge installation positions are individually detachable, and to provide, at any position, an enough space for the image-forming process cartridge of black Bk, which has a large-capacity toner container. Thus, size and cost of the image forming apparatus increase.